Electrical connectors can experience an impedance drop near the mating interface area of the connector. A side view of an example embodiment of an electrical connector is shown in FIG. 1A. The mating interface area is designated generally with the reference I and refers to the mating interface between the header connector H and the receptacle connector R.
FIG. 1B illustrates the impedance drop in the mating interface area. FIG. 1B is a reflection plot of differential impedance as a function of signal propagation time through a selected differential signal pair within a connector as shown in FIG. 1A. Differential impedance was measured at various times as the signal propagated through a first test board, a receptacle connector (such as described in detail below) and associated receptacle vias, the interface between the header connector and the receptacle connector, a header connector (such as described in detail below) and associated header vias, and a second test board. Differential impedance was measured for a 40 ps rise time from 10%-90% of voltage level.
As shown, the differential impedance is about 100 ohms throughout most of the signal path. At the interface between the header connector and receptacle connector, however, there is a drop from the nominal standard of approximately 100 Ω, to an impedance of about 93/94 Ω. Though the data shown in the plot of FIG. 1B is within acceptable standards (because the drop is within ±8 Ω of the nominal impedance), there is room for improvement.
Additionally, there may be times when matching the impedance in a connector with the impedance of a device is necessary to prevent signal reflection, a problem generally magnified at higher data rates. Such matching may benefit from a slight reduction or increase in the impedance of a connector. Such fine-tuning of impedance in a conductor is a difficult task, usually requiring a change in the form or amount of dielectric material of the connector housing. Therefore, there is also a need for an electrical connector that provides for fine-tuning of connector impedance.